Advanced Study on Remote Measurement of Chemical Composition of Volcanic Gas by Infrared Spectroscopy

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Authors have been trying to develop a new remote measuring system to determine chemical compositions of volcanic gases by infrared absorption spectroscopy since early 1990' s, and first succeeded to determine the HCl/S0_2 ratio. Thereafter, more species such as CO, C0_2, COS, HF and SiF_4 could be detected. This research project aims to improve this system in order to apply more commonly, more easily and/or more quickly with keeping higher sensitivity. In 2002, a new FT-IR spectrometer (manufactured by Midac Co.) with high sensitivity was purchased and a new observation system for field use was made up. In 2003, after testing the specification of this system and calibrating each component in the laboratory, field observations were carried out at Aso and Sakurajima volcanoes. In our previous observations, we used hot rocks or hot ground behind the volcanic gas as an infrared light source. Instead, scattered solar light was first applied as an infrared light source, obtaining clear absorption spectra of SO_2 and HCI.